Automatic cutout switch with bimetallic strip control



Nov. 11 1941. v 'H. SCHACHTNER 2,262,205

AUTOMATIC CUTQUT SWITCH WITH BIMETALLIC STRIP CONTROL Filed Sept. 14,- 1957 L IN VENTOR. Mia/12k 'salukfnm.

. hiA'I'IORNEYS I wPsiseisdiN 941 AUTOMATIC CUTOUT SWITCH WITH BIIVIETALLIC STRIP CONTROL Heinrich Schachtner, Schwetzingen, Baden, Germany, assignor to Stotz-Kontakt,

Gesell-- schait mit beschriinkter Baftung, Mannheim- Necharau, Germany, a corporation of Germany Amanda September 14, 1937, Serial No. 163,711 In Germany September 21, 1936 3 Claims.

My invention relates to automatic cut-out switches, such as are employed for protecting electric circuits from overload by responding at a given current magnitude. In particular, my invention relates to this type of cut-out switch in Y which a bimetallic strip is employed which actuates the cut-out mechanism when the strip is heated by the excess current.

Bimetallic strip arrangements for actuating automatic switches for rapid opening and closing are already known. For instance in one prior art construction, thebi-metallic strip is fixed at one of its ends and carries pivotally attached to its free end a switch lever which pulls the circuit contacts open. Between this lever and the bimetallic strip is interposed a tilting spring in such manner that the strip and the switch lever form a toggle joint normally held by the spring in a stable position. in another similar prior art type, the bimetallic strip fixed at one end forms a toggle joint with a lever connected endwise with the other strip end and in which a spring,

tends to axially shift the lever into one or the other extreme position. In this case the movable contact is connected by way of a spring to the metal. strip. Both of these prior art forms are actuated by the bending or deformation oi the bimetallic strip, through heating by the excess current load up to the point where the spring power thus produced in the strip overcomes that of the tilting spring, so' that the toggle joint is tripped and snaps from one extreme position over into the other extreme position.

The disadvantage of these prior art arrangements is that diiliculty is encountered to provide the automatic switch with a so-called trip-free mechanism, that is, a mechanism which prevents tampering with the snap movement as well as forcibly -holding the contacts in circuit-closing position during the occurrence or continuance of an excess load. Such a trip-free mechanism also is unnecessary with the above-mentioned known stallations, or motors, and the like, and consists in providing these breakers with a bimetallic strip and a coacting, spring-biased tilting lever in such a way that the strip forms part of a trip-free snap action mechanism. Especially according to the invention, a locking cam is arranged which is movable in the direction of an axis disposed substantially at right angles to the strip axis and tends to move, for instance by a spring, into the operating path of the bimetallic strip after the latter has responded to an overload, but is prevented by the strip from doing so in the closed contact position of the switch. As soon as the strip has moved into contact opening position, this cam is thrown in front of the bimetallic strip and prevents the latter, after it has cooled off, from returning the toggle joint into contact closing position, until the'cam is withdrawn from outside, such as by hand. The great advantage of this arrangement resides in the fact that a trip-free mechanism with snap action is attained by an especially simple structure of great reliability, as will become apparent from the following description of an embodiment of my invention in connection with the accompanying light construction that it requires so little power for its operation, that it does not perceptibly interfere with the automatic opening operation of the contact mechanism, and that it is easily operated from outside to unlock the open contacts and to restore thedevice entirely to its automatic tendency to close, plfilfifldd the strip has sufliciently cooled.

thermostatic control devices, since they are em- My invention is illustrated in the accompanying drawing in which Fig. 1 shows the switch in side elevation, partly in section and with the protecting casing removed.

Fig. 2 shows a plan View of Fig. l with the contacts in closed position, and h Fig. 3 a similar plan view with the contacts locked in open position,

Referring to these figures, on the switch base plate a, which may consist of any insulating material appropriate for the purpose, are mounted spaced apart the binding posts 1) and c. On

post b is fixed a contact spring d which carries one of the switch contacts e at its outer end, and which is shaped so that it tends to throw this contact beyond the center line between the binding posts as shown in Fig. 3. On post 0 is fixed one end of a bimetallic strip 1 which carries" the other switch contact 9 near its free end. A suitable distance beyond the free end of strip I is mounted on the base afixed pivot stud h, which suppQrts pivotally attached to it a toggle lever i provided with a longitudinally movable exten-' sion element 2. A spring j between extension i these contacts apart (Fig.3) The normal spring tendency of strip 1 when cold moves the toggle joint intothe contact closing position shown in Fig. 2, ii the joint should be in open position.

On base a adiacentto strip andbetween its contact a and binding post'c-is mounted a push pin it. This pin extends at right anglesto'the longitudinal axis of strip 1 and is longitudinally guided at its lower end in base a and near its upper end in a plate 0, which forms part of the base structure. The upper end of pin it carries that the bimetallic strip be directly heated by the current. It may also be indirectly heated. Furthermore, it is immaterial whether the locking element It is located in the path of the bimetallic strip orinthe path of the other toggle joint ole-- ment, for instance 2''. Lastly, it is also immaterial how the element which moves contact a'into and a hand push knob m, and betweenthis knob and v guide plate 0 a compression spring n is disposed on the pin, tending to throw the latter upwardly in Fig. 1, and toward the observer in Figs. 2 and 3. 0n pin k is mounted acam element p which is normally, i. e. when the switch is closed, disposed in a recess of base a (see Fig. 1) and, due to the tension of spring n, rests lightly against the edge of bimetallic strip 1 (Fig. 2), which latter thus prevents it from leaving its recess. If the toggle joint is in the other extreme position with the contacts opened, as shown in Fig. 3,

strip is removed from cam p and the latter is thrust by spring n into the path of strip fpso that the latter comes to rest upon the periphery of the cam. The operation of this device is as follows. If, with the toggle joint in contact closing position as in Fig.2, an overload occurs in the circuit; the. current which passes through strip j heats the latter so that it bends and carries the toggle joint over its dead point from the position Fig. 2 into the position Fig. 3, whereby the contacts are quickly opened only after the joint passes the dead point, due to the tendency I of spring a to follow contact g partway with its contact e and until the joint snaps into the open contact position. Cam p now. moves in front of strip f as described, so that even when the latter cools, it is prevented from returning. the.

toggle joint into contact closing position. Only by depressing push button m is cam p removed from the path of strip f and the latter, following its normal spring tension, snaps the toggle joint back into. the contact closing position. This par-.

- ticular arrangement oi the arresting device for the toggle joint in open position has the advantage that pressure which may be exerted from outside against the push button m when the switch is closed, does not prevent the toggle joint from operating in caseof overload. The arrangement therefore forms an eflective and reliable- Obvious modifications may be made or the constituent elements of this switch within'th'e scope.

view:

of the invention. Forlnstanoe it is notv out 0! 01081118 position is' constructed, 1. e. whether it is a two-element toggle joint, such as is shown in the drawing as an example, or any kind of contact moving device including a thermostatically operating bimetallic strip as the source of motion.

I claim:

tection, comprising acontact arrangementan overload-responsive bimetallic strip for controlling said contact arrangement, and a pivotally mounted lever yieldingly engaging said strip to. form a toggle joint designed to effect a snap movement of said contact arrangement upon the heating by an overload and the cooling of said strip, in combination with a locking element disposed to move into the path of said toggle joint and arranged to be normally held by said joint in inoperative position when the joint is in contact-closing position, means for automatically moving said element into the path of said joint after the latter has moved into contact-opening position to prevent said joint from returning into contact-closing position, and outside means for removing said locking means from said joint path topermit the return of said joint into contactclosing position.

2. A trip-free circuit breaker for overload protection, comprising a snap action contact mechanism, an over lgad-responsive bimetallic strip de- -signedto vary its inovingtendenc in dependence uponthe occurrence of an overloa sa ti strirn forming an actuating part of said contact mechanism, a locking element disposed to be moved into the path of said mechanism and arranged to be held by said mechanism in inoperative position when said mechanism is in contact-closing position, spring means forautomatically moving sition.

3. A trip-free circuit breaker for overload protection, comprisingtwo contacts. a bimetallic strip for actuating one of said contacts, and a pi'votallymounted lever yieldingly engaging said strip endwise toform 'a' toggle joint designed to eflect a contact opening and closing snap move- Y ment of said lattercontact by the heating and cooling respectively of said bimetallic strip due to overload conditions, in combination with an axially slidable locking pin disposed adjacent and transversely'to said strip intermediate its ends,

. said pin having a cam resting laterally against the edge oi said strip when the latter is in contact-closing position, a spring tending to hold said cam against said strip so as to-ca'use said cam to automatically move transversely into the operating path of said strip when the latter has moved into contact-opening position to prevent -its return 'into contact-closing podtion, and

manual resetting means for removing said cam from said strip path to permit the retum-oi said strip into contact-closing podtion'. 

